1. Field of the Invention
The present invention relates to a hazard display system in which a hazard display is driven with a signal sent from a vehicle end and flickers by a predetermined period.
2. Description of Relevant Art
The automotive vehicle has therein a plurality of control units, e.g. a main control unit associated with an instrument panel, an engine control unit associated with an engine installed in a front portion of the vehicle and connected to the main control unit, a trunk control unit associated with a rear trunk and connected to the main control unit, etc.
Such control units have their CPU's (central processing units) for processing input signals on current status of associated parts, elements or circumstances to output signals such as for control, drive, or display of information on the current status. The input signals may be data, commands, clocks, etc.
Typically, such the signals are supplied in the form of a multiplexed signal, such as a sequence of bit strings divided on a temporal axis, in a frequency field and/or by phase ranges. At a respective CPU, necessary bit strings are read from designated time slots, frequency bands or phase regions, and processed in a programmed order.
A conventional hazard display system includes: a hazard switch on an instrument panel; a pair of emergency flicker display lamps (hereafter "hazard lamp") to be placed or set on a road either in front of and behind the vehicle, as it is stopped on the road due to an accident or trouble; and a drive system for the front and rear hazard lamps that comprises a main control unit associated with the hazard switch, an engine control unit controlled from the main control unit for temporarily driving the front hazard lamp, and a trunk control unit controlled from the main control unit for temporarily driving the rear hazard lamp.
The drive control from the main control unit is effected by a combination of a hazard signal and a flicker synchronizing signal to be read from a multiplexed signal at each controlled control unit. The hazard signal inherently is responsible to have each hazard lamp illuminate with a luminosity. The flicker synchronizing signal is for having the hazard lamps synchronously flicker. They had played their rolls in dedicated or passive switching circuitry.
Neither the engine control unit nor the trunk control unit is dedicated for driving the hazard lamp. They have their routine tasks to be executed in different great numbers of steps at bit processing rates. The hazard signal may de defined by a starting rise and an ending fall. However, the flicker synchronizing signal has to interrupt a process of routine task, at one of programmed points therefor.
FIG. 1 shows a combination of time charts of concerned signals in the conventional hazard display system.
At first, a hazard switch is turned on by a manual operation, which is detected, and a detection signal is input to the main control unit, where it is processed to generate a hazard signal in combination with a flicker synchronizing signal, which signals are output from the main control unit in a multiplexing manner and transmitted via multiplex signal lines to the engine control unit in a front portion of a vehicle and the trunk control unit in a rear portion of the vehicle.
The flicker synchronizing signal has a predetermined period Ta of e.g. 700 ms, and keeps an on-state over half the period, where it is e.g. a 1, and an off-state over the remaining half, where it is e.g. a 0. The synchronizing signal comprises a sequence of occurrences of the on-state followed by the off-state, which combination is an occurrence unit and will sometimes be called "flicker synchronous signal" or simply "synchronous-signal".
A first synchronous signal is input to the engine control unit, where its 1's and 0's are sequentially held until they will be sequentially processed in a program having interrupted a current task program. The interrupting program generates a sequence of signal values corresponding to the 1's and another sequence of signal values corresponding to the 0's. A combination of the generated signal value sequences provides a first one of an occurrence unit of a lamp driving signal to be output to the front hazard lamp, which signal unit will sometimes be called "front drive signal" or simply "drive signal".
The first synchronous signal is followed by a second synchronous signal. They are alike. There is thus generated an analogous second front drive signal at a timing depending on e.g. an interruption associated therewith, which is not always the same as that of the first drive signal. The occurrence of the second drive signal defines an end of the first drive signal, which thus has a corresponding period T11. Likewise, the second drive signal will have another period T12 defined by a third front drive signal.
On the other hand, the first synchronous signal is input to the trunk control unit also, where its 1's and 0's are sequentially processed in another program flow having interrupted another current task program. Accordingly, there occurs a first rear drive signal having still another period T13, which drive signal will be followed by a second rear drive signal having yet another period T14.
The period Ta of flicker synchronous signal is short. A synchronous signal may have been fast processed at the engine control unit, when processed at the trunk control unit with a significant delay, as any effective signal value can be processed to generate an effective drive signal.
A pair of resultant front and rear flickers might have been for a stopped vehicle on a road and might resemble a tail lamp or head light of a distant running vehicle, when observed from a vehicle traveling the road in the night.